[Anti-tumor effect of total body irradiation of low doses on WHT/Ht mice].

The effect of low dose (0.05-1.0 Gy) of total body irradiation (TBI) on non-tumor bearing and tumor bearing mice were investigated. Mice received TBI of 0.1 Gy during 6-12 hours before tumor cell inoculation demonstrated to need larger number of tumor cells (approximately 2.5 times) for 50 per cent tumor incidence, compared to recipient mice not to receive TBI. On the other hand, in tumor bearing mice given 0.1 Gy of TBI only tumor cell killing effect was not detected, however enhancement of tumor cell killing effect and prolonged growth delay were observed when tumor bearing mice were treated with 0.1 Gy of TBI in combined with local irradiation on tumors, especially cell killing effect was remarkable in dose range over 6 Gy of local exposure. The mechanism of the effect of 0.1 Gy TBI is considered to be host mediated reactions from the other our experimental results.